Paper manufacture



Patented Oct. 16, 1934 PATENT OFFICE PAPER MANUFACTURE Harold RobertRafton, Andover, Mass, assignor to Rafiold Process Corporation, acorporation of Massachusetts No Drawing. Application December 6, 1932,Serial No. 646,025

19 Claims.

This invention relates to the manufacture of paper filled with alkalinefiller.

The principal object of this invention is to produce paper substantiallyfree from discoloration, which paper contains alkaline filler andfibrous material capable of discoloration by alkaline filler.

An important object is to produce substantially unsized paper filledwith alkaline filler.

A further object is to produce substantially unsized paper filled withalkal ne filler, the surface of which paper has a different pH valuethan the alkaline filler itself.

A further object is to produce substantially unsized paper filled withalkaline filler, the surface of which paper is substantiallynon-alkaline.

Other objects and advantages of my invention will become apparent duringthe course of the following description.

In my copending application Serial No. 501,674, filed December 11, 1930,now Patent 1,922,325, granted August 15, 1933 I disclose a method ofmanufacturing sized paper filled with alkaline filler by the applicationof size and size precipitant to a paper web containing alkaline filler.Alternatively the precipitant may be applied to the paper mix and thesize to the web, or the size to the paper mix and the precipitant to theweb, or precipitated sizing may be applied to the web.

In my copending application Serial No. 644,909, filed November 29, 1932,I disclose a method of manufacturing sized paper filled with alkalinefiller wherein undeveloped, deteriorated or destroyed sizing isdeveloped, or sizing is enhanced or preserved, by the application of asizing affecting agent to a paper web containing alkaline filler.

The present invention deals with a method similar to that employed in mylast mentioned copending application, namely with the applica tion to afibrous web containing alkaline filler of an agent suitable foraffecting the web in the desird manner. In the present invention,however, I am concerned with paper which contains material, particularlyfibrous material, capable of being discolored by alkaline filler, and/orwith substantially unsized paper.

In the manufacture of paper filled with alkaline filler, fibrousmaterial may be used in certain cases which is not substantially allcellulose but which contains a portion and in some cases a considerableproportion of non-cellulo-sic material. This material when in contactwith alkaline filler, especially at the temperature of the paper machinedrying cylinders, has in certain instances a tendency to becomeyellowish or brown or otherwise to change from the color it possesseswhen originally employed. An example of such a fibrous stock is what isknown as ground wood, which is a fibrous material obtained from wood bymechanical grinding processes, and which has ordinarily received nochemical treatment. There are other fibrous materials obtained byso-called semi-chemical processes, which contain a considerable portionof the non-cellulosic constituents of the cellulose-containing sourcesfrom which the fibrous materials have been derived, and such fibrousmaterials in certain cases are also subject to discoloration by thealkalinity of the alkaline filler under similar conditions. In othercases fibres which are known as chemical fibres, that is, which havebeen derived from the original cellulose-containing material by arelatively drastic chemical treatment which removes the major portion ofthe non-cellulosic content of the original cellulose-containing materialemployed, may contain residual portions of non-cellulosic material whichmay be subject to similar discoloration by alkaline filler. Or any ofthe classes of fibres mentioned above may have associated. therewithcertain residues or constituents derived from the various processes towhich the fibre has been subjected, which when contacting with alkalinefiller, especially on the driers, may cause a discoloration; or even incertain cases the cellulosic constituent itself in contact with alkalinefiller may cause a. discoloration. Moreover, in certain cases in themanufacture of paper filled with alkaline filler certain coloringmatters such as pigments or dyes may be employed which are attacked byalkaline filler, particularly at the temperature of the driers.

It is an object of the present invention substantially to prevent thediscoloration in certain papers which may result from the reaction between alkaline filler and fibrous material or material associated withthe fibrous material, or substantially to restore the original color incase such discoloration has taken place, also substantially to restorethe color value of or substantially to prevent the deterioration ofcoloring matter affected by alkaline filler: all in the presence ofalkaline filler.

In the manufacture of substantially unsized paper filled with alkalinefiller, the paper produced is more or less alkaline in reaction, and ithappens that in certain cases this alkaline reaction of the papersurface has an unfavorable effect on certain inks, colors and the like,and thus such papers at times are at a disadvantage compared with papersfilled with nonalkaline filler. Thus, it will be apparent that theproduction of a paper filled with alkaline filler having a surfacereaction less alkaline than the alkaline filler with which it is filled,or even having a substantially non-alkaline surface reaction, that isone which is either neutral or in some cases acid, will result in theobtaining ofsubstantially improved results with such papers. It is anobject-of this invention to provide a method of manufacturing paperfilled with alkaline filler, which paper possesses a surface reaction ofa different pH value from its central portion, for example the surfacereaction may be only mildly alkaline, that is, less alkaline than thealkaline filler from which it is made, or even in some casessubstantially non-alkaline, i. e. either neutral or acidic.-

In the preferred practice of my invention I form a web containingfibrous material and alkaline filler, and to this web I apply a webaffecting agent.

One illustrative example of the practice of my invention is as follows:I mix in a beater or other suitable mixing device alkaline filler andfibrous material susceptible of discoloration by alkaline filler, suchas groundwood. There may also be present in the furnish other fibrousmaterial such as sulphite pulp or the like, which may if desired besubstantially non-susceptible of discoloration by alkaline filler. Themix may also if desired contain other ingredients such as sizing agent,or sizing agent and size precipitant. After giving the mix the properpreliminary preparation, it becomes ready for delivery to a web-formingdevice and when it is run off on such device a web containing alkalinefiller is produced. To this web I apply a web affecting agent and bythis means the paper which would otherwise be discolored is eitherprevented from being substantially discolored or has its discolorationsubstantially discharged.

Another illustrative example, in this case one in which I substantiallymaintain in, or restore to, a web the desired color, in which webalkaline filler is present in associationwith a dye or pigment capableof being affected by alkaline filler, is as follows: I mix fibrousmaterial and alkaline filler in a beater or other suitable mixingdevice, together with a dye or pigment capable of being affected byalkaline filler. There may be present also if desired other ingredientssuch as sizing agent, or sizing agent and size precipitant. I thensubject the mix to the desired treatment, and run it off on aweb-forming device to form a web which contains alkaline filler and thedye or pigment capable of being affected by alkaline filler. To this webwhich would otherwise have the improper or deteriorated color value, Iapply a web affecting agent whereupon the color of the dye or pigment issubstantially maintained at, or restored to, its desired color value.

Another illustrative example of practicing my invention in the casewhere I desire to produce substantially unsized paper filled withalkaline filler, and where I desire to produce a paper having a lessalkaline surface reaction than the paper would have if it were nottreated according to my invention, is as follows: I mix fibrous materialand alkaline fillerin the heater or other suitable mixing device, addingif desired an agent, preferably an acidic material such as alum, or sizein an amount insuflicient to impart a substantial degree of sizing tothe resulting paper, and if desired a precipitant therefor. I then givethe mix the desired treatment and run off the same on a web-formingdevice. There is thus formed a web containing alkaline filler, and tothis web I apply a suitable web affecting agent, whereupon the paperproduced will be found to have a less alkaline surface reaction than ifthe web affecting agent had not been applied.

In any of the above examples other papermaking ingredients may be addedas desired such as starch and the like. It will also be understood thatin any or all of these examples, the materials noted or other materialsdesired to be used therewith in the papermaking mix may be added inaccordance with the minimizing principle, that is, under conditionsfavoring the minimizing of the time and/or intimacy of contact of theconstituents of the mix, preferably at the dilute stage of thepapermaking operation, as described in a large number of my alreadyissued patents. According to such principle one or more of the variouspapermaking ingredients such as acidic material as alum, alkalinefiller, size, starch and the like may be added at the dilute stage ofthe papermaking process.

It will be understood of course that the above examples are merelyillustrative, and in no way limiting.

The web affecting agent which I employ for application to the webcontaining alkaline filler may be either gaseous, liquid or solid. Suchweb affecting agent must be of a nature which either reacts directlywith alkaline filler or which compensates for or inhibits the action ofalkaline filler on the fibrous material, coloring matter or the like.For instance acidic material in general may function, such for exampleas acetic acid or other organic or mineral acid as sulphuric orphosphoric acid or acid salt such as sodium bisulphate. The acids mayconveniently be applied to the web in liquid form preferably in aqueoussolution, but it is possible to apply at least 'certain of them such asformic, acetic, or hydrochloric acid in gaseous form; and also to applyacids or acid anhydrides which occur in gaseous form at temperatureswhich will not substantially injure cellulose fibre. Thus, for example,carbon dioxide or sulphur dioxide may be employed although in such casesthere should preferably be water or aqueous vapor present in order tomake them function properly.

Likewise the agent may be applied to the web in solid form for exampleas a solid acid. preferably finely powdered, such as solid organic acid,or powdered solid salts such as sodium bisulphate or the like may beused. In this case also water should preferably be present in the web toaffect the solution of the agent in order that it may have a propereifect on the web. Among other agents which I may employ in addition tothose mentioned are metallic compounds, preferably soluble, such forexample as sodium bisulphate and the like, which may be non-acid, orwhich may be acid, such as aluminum sulphate (ordinary alum) 140 as myweb affecting agent and because of convenience of handling it, I preferto apply it in aqueous solution.

The application, i. e. exposure, of the web affecting agent in gaseousor vapor form to the web may take place when the web is either in thewet or in the dry condition, but preferably when it is in the wetcondition, and will ordinarily require a container, hood or the like inwhich the web affecting agent may be exposed to the web. This maysuitably be provided by enclosing that part of the paper machine atwhich the exposure is to be made in a suitable hood or enclosure or thelike, which may be at atmospheric pressure, superatmospheric pressure,or subatmospheric pressure such as in a vacuum of suitable degree, asbest meets the particular case; or such agent may be applied to the webindependently of the paper machine in a special applying device.

The application of a liquid to the web, and this is my preferred method,may conveniently take place on the paper machine but here again as inthe case of the gaseous agent, the liquid may if desired be applied tothe web as a process independent of the paper machine. The abovestatements relative to place of application of a liquid are equallypertinent to the application of a solid web afiecting agent.

The application of the web affecting agent to the web may take placewhile the web is either in the wet or the substantially dry condition,but in my preferred practice of using a liquid agent such as alumsolution, I prefer to apply it to the already formed wet web after ithas left the web-forming device as this fits in most conveniently withthe ordinary papermaking operation and does not usually require specialdriers subsequent to the point of application of the agent, as might bethe case if the agent were applied to the dried or almost dry web. Itwill be understood, however, that where I speak of applying webaffecting agent to the web, I mean to include in the definition of weband as within the scope of my invention not only the already formed wetor dry web, but also "the web as it exists in its formative or formingstate at any point on the web-forming device between the point ofdelivery of the mix to the web-forming device and the point of deliveryof the formed web from the web-forming device; and of course it will beunderstood that such application may take place to either side of theweb, that is, either to the top or the bottom or to both.

In order to affect the alkaline filler near the surface more than thatat the center of the web, it is of course necessary to apply the webaffecting agent to the surface or surfaces of the web, but in certaincases such for example as where I wish to prevent discoloration ordecoloration by alkaline filler, it will of course be understood thatwhile the web is on the web-forming device the application of the webaifecting agent may in such instances include the case where the agentmay be introduced at the surface, as well as the case where the agentmay be introduced within the forming web by suitable introducingdevices.

In the application of the web afiecting agent I in solution to the web,any known form of device for applying liquids to a paper web may beemployed; for example the web may be passed through a trough or vatcontaining the solution, or the solution may be transferred to the webby brushes, for example rotary brushes, or by contact rolls, or bysupply boxes or rolls on the press rolls or other rolls, or by sprayingor the like. In the case of spraying, the spray may be relativelycoarse, or it may be very fine so as to be in the form of a mist, ifdesired. My preferred equipment is, however, arranged at the presses,preferably at the third press, or even better at the smooth rolls if themachine be equipped with such rolls. At such points, the web has lostmost if not all the water which it will lose by pressure and is in areasonably absorbent condition. Thus if the paper machine be equippedwith a third press roll which may be operated preferably without felts,two applying rolls contacting directly with the two third press rollsmay be used to apply the alum solution to the wet web. Of course it willbe understood that the contact rolls are supplied with the alum solutionby appropriate means such as immersion in supply boxes, troughs, or thelike, or by contact with other rolls, carrying the alum solution, orother suitable means. Optionally, and in certain cases thisv is adesirable procedure, the alum may be applied by an applying roll whichcontacts directly with the web itself and as will be apparent either inthis case or in the case of press roll application, the alum may beapplied either to one or both sides but the application to both sides ofthe web is the more general procedure.

In certain cases the web affecting agent may be applied by means of thefelt or feltsnormally contacting with the web on the paper machine, oreven by means of small independent travelling felt or felts, or belts,contacting with the web. In such cases the agent may be appliedpreviously to the felt or the like, or may be applied at the nip of thecontacting web and. felt. However, the application by roll or rolls isas simple as any and thoroughly practical, and hence is a veryconvenient one to use. In order to obtain more complete penetration ofthe web by the web affecting agent, the web may be led over a suctionbox, roll, or the like at or subsequent to the point where the webaffecting agent is applied to the opposite side of the web, particularlyin the case where the web affecting agent is applied only to one side ofthe web, or to the two sides at spaced intervals. If desired a felt,wire belt, or the like may be interposed between the Suction device andthe web to carry and/or support the web. In general the method ofapplication in any given case is that which is best adapted for use atthe particular point at which the agent is to be applied and should bechosen with regard to the particular conditions to be met in any givencase, all of which will be apparent to one skilled in the art.

As the agent is preferably applied continuously to the web, suitablemeans for supplying it to the applying device, for example pumps, shouldbe employed, and the amounts applied should preferably vary regularlywith the paper machine speed and be adjustable to the various grades andweights of paper run.

After the application to the web of the web affecting agent, the papermay be dried in the customary manner if desired and calendered orotherwise finished according to the type of paper being made. The resultof the application of this web affecting agent is, as the case may be,to produce a paper with a different surface reaction than wouldotherwise be produced, and/ or to produce a paper in which alkalinefiller and fibrous material and/or coloring matter susceptible todiscoloration or decoloration by alkaline filler is present, in whichthe color is substantially preserved or restored. In certain cases alsothe application of web aifecting agent to the web reduces any tendencyto stick at the press rolls, of course in such case the agent beingapplied before or at the press rolls; and also in certain cases if theagent is applied at the web-forming device a tendency in certain mixestoward foaming or filling up the dandy roll can be reduced.

It will be understood, of course, that my invention of restoring thecolor to, or preserving the color in, a web containing alkaline fillerand fibrous material capable of being deteriorated in color by alkalinefiller, differs in principle from the practice of the prevention ofdiscoloration of fibrous material by the impurities thereof, byacidification; as in my invention the co-presence of the discolorationand the alkaline filler responsible therefor prevents completeacidification of the admixture of the paper ingredients, such as ispossible only when no alkaline filler is present, and it was hithertobelieved to be impossible to prevent discoloration of fibrous materialunless complete acidification or at least neutralization was effected.

While I do not limit myself to the concentratron of alum solution to beapplied, and it will be apparent that the concentration required will inany event be influenced by machine speed, type of paper manufactured,and other variables well known to one skilled in the art, nevertheless Ican state that a 15 per cent. solutionhas been found to be satisfactoryfor my purpose, 'and this can be the one tried in practice first andthen adjustment of the concentration may be made either one way or theother. However in certain cases, for example if suction is to be appliedto the sheet to improve the penetration of the webaffecting agent, amuch more dilute solution may be employed for example 1 per cent. orthereabouts. Likewise the amount of alum to be applied is difiicult tostate definitely owing to the variation in conditions, and type of papermade, but it may vary in certain cases from a fraction of a per cent. onthe total furnish up to several per cent, and this quantity may beconveniently controlled by the agent applying device in conjunction withthe adjustment of the concentration of the solution applied.

It will be apparent that the application of the web afiecting agent tothe web, particularly if said agent be one which does not substantiallyre actwith alkaline filler, will merely result in the co-presence in theweb of the agent and the alkaline filler, or such amount of the agent asis not used up, for example by its web affecting action, or otherwise.Of course such amount of agent will in general be concentrated morenearly at one or both surfaces than at the central portion of the webaccording as the application has taken place to one or both surfaces.

However, if the web-affecting agent be one which reacts with alkalinefiller, such as an acidic reagent,'such action will result in a changein the chemical composition of the alkaline filler, at least on thesurface of the alkaline filler particles, the reaction taking place moreparticularly withthose particles of the alkaline filler which are nearthe superficial part of the web, this action taking place either at oneor both sides of the web according as the application of the agent ismade to one or both sides of the web; and in certain cases as will beapparent the pH value of the compound formed will be different from thatof the alkaline filler itself, in most cases less. For example, ifacetic acid be used as the agent and calcium carbonate as the filler, acertain amount of calcium acetate may be produced. On the other hand if,with calcium carbonate, an acid or an acid salt be used of which thecalcium salt is substantially insoluble, that corresponding salt will beformed. For example, if phosphoric acid or an acid phosphate be theagent used, calcium phosphate will be formed. If sulphuric acid or acidsulphate such as alum be used, calcium sulphate will be formed, as wellas aluminum hydroxide or other aluminum compound where alum is used.

By the term alkaline filler I mean substantially water insoluble fillerwhich when agitated in contact with freshly boiled distilled water, sayfor an hour, will impart a pH value to such water greater than 7.0, thatis, which will be on the alkaline side of the neutral point. Amongfillers in this group may be mentioned calcium carbonate, of which limemud from the causticizing process is one form; calcium carbonatemagnesium basic carbonate employed in the paper disclosed in my UnitedStates Patent No. 1,595,416, issued August 10, 1926; calcium carbonatemagnesium hydroxide disclosed in my United States Patent No. 1,415,391,issued May 9, 1922, and other substantially water insoluble normal orbasic carbonates of alkaline earth metals, (which expression is hereinintended to include magnesium), or compounds, double salts, or otherphysically associated mixtures of these with one or more other acidsoluble materials of a substantially water insoluble nature. By the termalkaline filler I also intend to include fibrous material and/or othermaterial such as paper coating constituents or the like containing oneor more compounds of the character referred to, such as old papers orsimilar papers, broke, or the like.

When I use the word paper herein, I use it in the broad sense to includeproducts of manufacture of all types and of all weights and thicknesses,which contain as an essential constituent a considerable amount ofprepared fibre and which are capable of being produced on a Fourdrinier,cylinder, or other forming, felting, shaping or molding machine.

Cross reference is hereby made to my copending application Serial No.672,901, filed May 25, 1933, having certain related subject matter, aswell as to my copending application, of which said application is a.division, namely application Serial No. 534,462, filed May 1, 1931, nowmatured into Patent'No. 1,914,526, issued June 20, 1933.

While I have described in detail various embodiments and examples of myinvention, it is to be understood that the details of procedure andequipment,.the proportions of ingredients, and the arrangement of stepsmay be widely varied without departing from the spirit of my inventionor the scope of the subjoined claims.

I claim:

1. Paper filled with alkaline filler including among its ingredientsalkaline filler and coloring matter capable of deterioration by alkalinefiller in the presence of moisture at the temperature of paper machinedriers, said coloring matter being present in substantiallyundeteriorated condition.

2. Paper filled with alkaline filler including among its ingredientsalkaline filler and fibrous material capable of discoloration byalkaline filler in the presence of moisture at the temperature of papermachine driers, said fibrous material being present in a conditionsubstantially free from discoloration.

3. Paper filled with alkaline filler and containing groundwood at leastone surface of which paper has a different pH value than the centralportion thereof.

4. Paper filled with alkaline filler and containing groundwood, at leastone surface of which paper is less alkaline than said alkaline filler.

5. Paper filled with alkaline filler and containing groundwood, saidpaper being less alkaline at at least one of its surfaces than it is inthe central portion thereof.

6. Paper filled with alkaline filler and containing groundwood, at leastone surface of which paper is substantially non-alkaline.

7. Substantially unsized paper filled with alkaline filler, at least onesurface of which has a different pH value than the central portionthereof.

8. Substantially unsized paper filled with alkaline filler, at least onesurface of which paper is less alkaline than saidalkaline filler.

9. Substantially unsized paper filled with alkaline filler, said paperbeing less alkaline at at least one of its surfaces than it is in itscentral portion.

10. Substantially unsized paper filled with alkaline filler, at leastone surface of which paper is substantially non-alkaline.

l1. Substantially unsized paper filled with alkaline filler, at leastone surface of which paper is acidic.

12. Substantially unsized paper filled with alkaline filler having aconversion product formed in situ from alkaline filler adjacent at leastone of the surfaces of said paper.

13. Substantially unsized paper filled with alkaline filler, theparticles of said filler near the surface of said paper having a coatingthereon comprising a compound of a lower pH value than said alkalinefiller, said compound having a higher concentration adjacent at leastone of the surfaces of said paper than it has at the central portion ofsaid paper.

14. Substantially unsized paper filled with alkaline filler, having asubstantially non-alkaline compound formed in situ from alkaline filleradjacent at least one of the surfaces of said paper.

15. Substantially unsized paper filled with alkaline filler, theparticles of said filler near the surface of said paper having a coatingof substantially non-alkaline compound thereon, said non-alkalinecompound having a higher concentration adiacent at least one of thesurfaces of said paper than it has at the central portion of said paper.l6. Substantially unsized paper filled with alkaline filler comprisingcalcium carbonate at least part of which is superficially coated with areaction product of a pH value different from said calcium carbonate,said reaction product being formed in situ.

17. Substantially unsized paper filled with alkaline filler comprisingcalcium carbonate at least part of which is superficially coatedwith'calcium sulphate.

18. Substantially unsized paper filled with alkaline filler, containingresidual substantially unaffected web affecting. agent adjacent atleast'one of the surfaces of said paper.

19. That step in the manufacture of paper, which paper includes amongits ingredients alkaline' filler and fibrous material capable ofdiscoloration by alkaline filler, comprising applying web affectingagent to a paper web including said alkaline filler and said fibrousmaterial.

HAROLD ROBERT RAFTON.

